He said: ‘It’s not a competition, it’s a challenge — that’s a huge difference.’

The motivational man wants 100 people to join him in a triathlon, which people can complete wherever they are, on whatever equipment they have.

Mar Hardman said: ‘Someone said to me “I have to go to work that day” but that doesn’t matter because they could cycle to work, and then do the run and swim after.’

Five people have already signed up, including two royal marines from HMS Drake.

He added: ‘As it’s 100 years since the start of the First World War it would be fantastic to get 100 people doing it on this date.’

He wants people to swim 1,914 metres (76.56 lengths of a 25m pool), cycle 28km (seven miles and then run seven km (four miles) on July 28.

Each of the number relates to the date that the First World War started – July 28, 1914.

‘It is enticing people to do a triathlon,’ he said.

‘Most triathlons are a competition and that can put people off, with this you are not competing against anyone other than yourself.’

All the money raised through sponsorship will go to the Poppy Appeal, something that is very important to John as he is part of the Royal British Legion Riders Branch — the motorcycling branch of the Royal British Legion.

Mr Hardman said: ‘The Royal British Legion are very close to my heart as it is the only British charity that looks after the whole of the British military and their families. They do such good work.’

The Royal British Legion Riders Branch has raised nearly £1m for the Poppy Appeal since it was formed in 2004 – of which he has raised at least £50,000.

Mr Hardman, who served at HMS Collingwood, said: ‘As an ex-PTI in the Navy, I like to get people out having a go. That’s my aim.’